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14 Feb 2005

Volume 86, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 86, 071101 (2005); http://dx.doi.org/10.1063/1.1862756 (3 pages)

Robert Horvath, Henrik C. Pedersen, Nina Skivesen, David Selmeczi, and Niels B. Larsen
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Monitoring of living cell attachment and spreading using reverse symmetry waveguide sensing

Robert Horvath, Henrik C. Pedersen, Nina Skivesen, David Selmeczi, and Niels B. Larsen

Appl. Phys. Lett. 86, 071101 (2005); http://dx.doi.org/10.1063/1.1862756 (3 pages) | Cited 27 times

Online Publication Date: 7 February 2005

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The effect of the attachment and spreading of living cells on the modes of a grating coupled reverse symmetry waveguide sensor is investigated in real time. The reverse symmetry design has an increased probing depth into the sample making it well suited for the monitoring of cell morphology. As a result, significant changes in the incoupling peak height and peak shape were observed during cell attachment and spreading. It is suggested that the area under the incoupling peaks reflects the initial cell attachment process, while the mean peak position is mostly governed by the spreading of the cells.
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87.85.Lf Tissue engineering
87.17.-d Cell processes
87.50.W- Optical/infrared radiation effects
42.79.Gn Optical waveguides and couplers

Thermal relaxation trimming for enhancement of extinction ratio in electro-optic polymer Mach-Zehnder modulators

Suntak Park, Jung Jin Ju, Seung Koo Park, Myung-Hyun Lee, and Jung Yun Do

Appl. Phys. Lett. 86, 071102 (2005); http://dx.doi.org/10.1063/1.1864236 (3 pages) | Cited 7 times

Online Publication Date: 7 February 2005

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We propose and demonstrate a trimming method to enhance extinction ratio in an electro-optic (EO) polymer modulator with a Mach-Zehnder interferometer structure. In order to adjust the power splitting ratio at Y-branches, which is a main factor determining the extinction ratio, our method is exploited by using a change of the refractive index of the poled EO polymer due to thermal relaxation. The trimming is controlled by heating the Y-branch area via a heater. By using the thermal relaxation trimming, the extinction ratio in the adjusted EO modulator is enhanced by more than 7 dB without excess loss.
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42.79.Hp Optical processors, correlators, and modulators
07.60.Ly Interferometers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Experimental demonstration of fiber-accessible metal nanoparticle plasmon waveguides for planar energy guiding and sensing

Stefan A. Maier, Michelle D. Friedman, Paul E. Barclay, and Oskar Painter

Appl. Phys. Lett. 86, 071103 (2005); http://dx.doi.org/10.1063/1.1862340 (3 pages) | Cited 61 times

Online Publication Date: 7 February 2005

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Experimental evidence of mode-selective evanescent power coupling at telecommunication frequencies with efficiencies up to 75% from a tapered optical fiber to a metal nanoparticle plasmon waveguide is presented. The waveguide consists of a two-dimensional square lattice of lithographically defined Au nanoparticles on an optically thin silicon membrane. The dispersion and attenuation properties of the waveguide are analyzed using the fiber taper. The high efficiency of power transfer into these waveguides solves the coupling problem between conventional optics and plasmonic devices and could lead to the development of highly efficient plasmonic sensors and optical switches.
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42.81.Pa Sensors, gyros
42.79.Gn Optical waveguides and couplers
42.81.Dp Propagation, scattering, and losses; solitons
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography

100% phosphorescence quantum efficiency of Ir(III) complexes in organic semiconductor films

Yuichiro Kawamura, Kenichi Goushi, Jason Brooks, Julie J. Brown, Hiroyuki Sasabe, and Chihaya Adachi

Appl. Phys. Lett. 86, 071104 (2005); http://dx.doi.org/10.1063/1.1862777 (3 pages) | Cited 69 times

Online Publication Date: 8 February 2005

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We demonstrate that three Ir(III) complexes used as principal dopants in organic electrophosphorescent diodes have very high photoluminescence quantum efficiency (ηPL) in a solid-state film. The green emitting complex, fac-tris(2-phenylpyridinato)iridium(III) [Ir(ppy)3], the red-emitting bis[2-(2′-benzothienyl)pyridinato-N,C3′] (acetylacetonato)iridium(III) [Btp2Ir(acac)], and the blue complex bis[(4,6-difluorophenyl)pyridinato-N,C2](picolinato)iridium(III) (FIrpic) were prepared as codeposited films of varying concentration with 4,4′-bis(N-carbazolyl)-2,2′-biphenyl, a commonly used host material. The maximum ηPL values for Ir(ppy)3, Btp2Ir(acac), and FIrpic were, respectively, 97%±2% (at 1.5 mol%), 51%±1% (at 1.4 mol%), and 78%±1% (at 15 mol%). Furthermore, we also observed that the maximum ηPL of FIrpic reached 99%±1% when doped into the high triplet energy host, m-bis(N-carbazolyl)benzene, at an optimal concentration of 1.2 mol%.
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85.60.Jb Light-emitting devices
78.66.Li Other semiconductors
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials

Growth and in situ annealing conditions for long-wavelength (Ga, In)(N, As)/GaAs lasers

B. Damilano, J. Barjon, J.-Y. Duboz, J. Massies, A. Hierro, J.-M. Ulloa, and E. Calleja

Appl. Phys. Lett. 86, 071105 (2005); http://dx.doi.org/10.1063/1.1863433 (3 pages) | Cited 10 times

Online Publication Date: 8 February 2005

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The conjugated effect of growth temperature and in situ thermal annealing on the photoluminescence properties of In0.4Ga0.6As0.985N0.015/GaAs quantum wells (QWs) grown by molecular-beam epitaxy has been investigated. The interplay between growth temperature and annealing effects is such as the optimum growth temperature is not the same for as-grown and annealed samples. By using the combination of a low growth temperature and a high in situ annealing temperature, separate confinement heterostructure laser diodes with a single In0.4Ga0.6As1−xNx (x = 0.015–0.021)/GaAs QW have been grown. The broad area devices emit from 1.34 to 1.44 μm at room temperature with a threshold current density of 1500–1755 A/cm2.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Cc Kinetics of defect formation and annealing
78.67.De Quantum wells
78.55.Cr III-V semiconductors

Ultraviolet poling of pure fused silica by high-intensity femtosecond radiation

Costantino Corbari, Peter G. Kazansky, Stephen A. Slattery, and David N. Nikogosyan

Appl. Phys. Lett. 86, 071106 (2005); http://dx.doi.org/10.1063/1.1868075 (3 pages) | Cited 5 times

Online Publication Date: 8 February 2005

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We demonstrate UV poling of a pure fused silica sample by applying to it an electric field of 200 kV/cm and irradiating it with high-intensity ( ∼ 40 GW/cm2) femtosecond (220 fs) laser pulses at 264 nm.
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78.47.-p Spectroscopy of solid state dynamics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
72.40.+w Photoconduction and photovoltaic effects
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Numerical extraction of distributions of space-charge and polarization from laser intensity modulation method

Enis Tuncer and Sidney B. Lang

Appl. Phys. Lett. 86, 071107 (2005); http://dx.doi.org/10.1063/1.1865333 (3 pages) | Cited 10 times

Online Publication Date: 8 February 2005

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The Fredholm integral equation of the laser intensity modulation method is an ill-conditioned problem with multiple solutions. An approach based on an application of the Monte Carlo technique and a least-squares solver is developed and tested on simulated data containing both Gaussian and white noise. Good agreement between the original polarization and the estimated one was found. The influences of bin size and spacing, and errors in material properties, are discussed. It is shown that the presented approach is an alternative to other data analysis techniques in the literature based on regularization algorithms.
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77.22.Jp Dielectric breakdown and space-charge effects
77.22.Ej Polarization and depolarization
42.60.Fc Modulation, tuning, and mode locking

Electroluminescent three-dimensional photonic crystals based on opal–phosphor composites

Saveliy F. Kaplan, Nelli F. Kartenko, Dmitry A. Kurdyukov, Alexander V. Medvedev, and Valery G. Golubev

Appl. Phys. Lett. 86, 071108 (2005); http://dx.doi.org/10.1063/1.1866223 (3 pages) | Cited 2 times

Online Publication Date: 8 February 2005

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The composites opal–Zn2SiO4:Mn and opal–GaN–ZnS:Mn were synthesized by chemical bath deposition. These materials are perfect three-dimensional photonic crystals which produce effective fluorescence at room temperature when excited by an alternating current electric field. The electroluminescence spectrum is considerably modified by the photonic band gap to become anisotropic in accordance with the photonic band gap angular dispersion.
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42.70.Qs Photonic bandgap materials
81.05.Ea III-V semiconductors
78.60.Fi Electroluminescence
78.55.Cr III-V semiconductors
81.10.Dn Growth from solutions

Buried waveguides in terahertz quantum cascade lasers based on two-dimensional surface plasmon modes

J. Alton, S. S. Dhillon, C. Sirtori, A. de Rossi, M. Calligaro, S. Barbieri, H. E. Beere, E. H. Linfield, and D. A. Ritchie

Appl. Phys. Lett. 86, 071109 (2005); http://dx.doi.org/10.1063/1.1866639 (3 pages) | Cited 12 times

Online Publication Date: 9 February 2005

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A scheme for buried waveguides in terahertz quantum cascade lasers is demonstrated by combining a surface plasmon mode with ion implantation. The mode is bound to a metal strip deposited on the surface of the device that confines the light in both vertical and lateral directions without any etching requirements. Ion implantation is used to confine the current that selectively pumps the active region. Electrical and optical measurements demonstrate this two-dimensional confinement. Further, by taking advantage of the lower losses and a reduced thermal resistance, laser action is achieved in continuous wave up to 77 K.
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42.55.Px Semiconductor lasers; laser diodes
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

100% fluorescence efficiency of 4,4′-bis[(N-carbazole)styryl]biphenyl in a solid film and the very low amplified spontaneous emission threshold

Takanori Aimono, Yuichiro Kawamura, Kenichi Goushi, Hidetoshi Yamamoto, Hiroyuki Sasabe, and Chihaya Adachi

Appl. Phys. Lett. 86, 071110 (2005); http://dx.doi.org/10.1063/1.1867555 (3 pages) | Cited 28 times

Online Publication Date: 9 February 2005

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We examined the amplified spontaneous emission (ASE) characteristics of fluorescent styrylbenzene derivatives doped into a 4,4′-di(N-carbazolyl)biphenyl (CBP) host. In particular, 4,4′-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) demonstrated an extremely low ASE threshold of Eth = 0.32±0.05 μJ/cm2. We observed that the 6 wt %-BSB-Cz:CBP film has an ultimate photoluminescence (PL) quantum efficiency of ϕPL = 100% and a short transient lifetime of τf = 1.0±0.1 ns, leading to a large radiative decay rate of kr = 1×109 s−1. We demonstrated that the extremely low ASE threshold originated from the large radiative decay rate of BSB-Cz.
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78.66.Li Other semiconductors
78.45.+h Stimulated emission
78.55.Kz Solid organic materials

Tunable hollow waveguide Bragg grating with low-temperature dependence

Yasuki Sakurai, Yasushi Yokota, Akihiro Matsutani, and Fumio Koyama

Appl. Phys. Lett. 86, 071111 (2005); http://dx.doi.org/10.1063/1.1867557 (3 pages) | Cited 7 times

Online Publication Date: 9 February 2005

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We demonstrate a tunable hollow waveguide Bragg grating with low-temperature dependence. We fabricated a distributed Bragg reflector consisting of a grating loaded slab semiconductor hollow waveguide with a variable air-core. A change in an air-core thickness enables us to achieve a tunable propagation constant of several percents resulting in a large shift of several tens of nanometers in Bragg wavelength. We demonstrate 10 nm continuous wavelength tuning of a peak reflectivity. This value corresponds to a propagation constant change of 0.64%, which is larger than that of thermo-optic effects or electro-optic effects. The measured temperature sensitivity of the peak wavelength is as low as 0.016 nm/K, which is seven times smaller than that of conventional semiconductor waveguide devices.
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42.79.Gn Optical waveguides and couplers
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings
42.82.Cr Fabrication techniques; lithography, pattern transfer

AlGaAs emitter/GaAs barrier terahertz detector with a 2.3 THz threshold

M. B. M. Rinzan, A. G. U. Perera, S. G. Matsik, H. C. Liu, Z. R. Wasilewski, and M. Buchanan

Appl. Phys. Lett. 86, 071112 (2005); http://dx.doi.org/10.1063/1.1867561 (3 pages) | Cited 20 times

Online Publication Date: 9 February 2005

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A heterojunction interfacial work function internal photoemission (HEIWIP) detector with a threshold frequency (f0) of 2.3 THz (λ0 = 128 μm) is demonstrated. The threshold limit of ∼ 3.3 THz (92 μm) due to the Al fraction being limited to ∼ 0.005, in order to avoid control and transition from alloy to isoelectronic doping behavior, was surpassed using AlGaAs emitters and GaAs barriers. The peak values of responsivity, quantum efficiency, and the specific detectivity at 9.6 THz and 4.8 K for a bias field of 2.0 kV/cm are 7.3 A/W, 29%, 5.3×1011 Jones, respectively. The background-limited infrared photodetector temperature of 20 K with a 60° field of view was observed for a bias field of 0.15 kV/cm. The f0 could be further reduced toward ∼ 1 THz regime ( ∼ 300 μm) by adjusting the Al fraction to offset the effect of residual doping, and/or lowering the residual doping in the barrier, effectively lowering the band bending.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.uj III-V and II-VI semiconductors

Thin-film InGaN multiple-quantum-well light-emitting diodes transferred from Si (111) substrate onto copper carrier by selective lift-off

Baijun Zhang, Takashi Egawa, Hiroyasu Ishikawa, Yang Liu, and Takashi Jimbo

Appl. Phys. Lett. 86, 071113 (2005); http://dx.doi.org/10.1063/1.1863412 (3 pages) | Cited 9 times

Online Publication Date: 9 February 2005

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Crack-free thin-film InGaN multiple-quantum-well light-emitting diodes (LEDs) were successfully transferred from the original Si (111) substrate onto copper carrier by means of metal-to-metal bonding and the selective lift-off (SLO) technique using wet-chemical etching. Crystalline quality was investigated by x-ray diffraction and photoluminescence measurements. No deterioration was found in the thin film after substrate removal due to the fact that the SLO technique minimizes the residual strain relaxation. Substrate removal eliminates not only the substrate absorption but also the large band offset between the AlN buffer layer and substrate. In conjunction with inserting a metal reflector between the LED structure and the copper carrier, the performances of the LED fabricated on the substrate removal region were significantly improved. The operating voltage at 20 mA and the series resistance was 3.6 V and 27 Ω, respectively. The optical power revealed an increase of 49% compared to the LED before substrate removal.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
68.65.Fg Quantum wells
78.67.De Quantum wells
81.65.Cf Surface cleaning, etching, patterning

High extinction ratio antiresonant reflecting optical waveguide-type polarizers with large core diameter

J. Y. Lin and A. K. Chu

Appl. Phys. Lett. 86, 071114 (2005); http://dx.doi.org/10.1063/1.1865336 (3 pages)

Online Publication Date: 9 February 2005

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An optical polarizer based on antiresonant reflecting optical waveguide (ARROW) structure is presented. The advantage over conventional ARROW devices is the fact that high extinction ratio of the proposed polarizer can be obtained even with a large core diameter. This comes into effect because loss discrimination against TM modes is dramatically enhanced due to birefringence of the polyimide core. In addition, the loss discrimination can be further increased by reducing the thickness of the core at the first antiresonant condition. The measured extinction ratio and insertion loss of a 2-cm-long polyimide/Ta2O5/SiO2 ARROW polarizer are 40 dB and 2.2 dB, respectively.
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42.79.Ci Filters, zone plates, and polarizers
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics

Lifetime of photogenerated carriers in silicon-on-insulator rib waveguides

D. Dimitropoulos, R. Jhaveri, R. Claps, J. C. S. Woo, and B. Jalali

Appl. Phys. Lett. 86, 071115 (2005); http://dx.doi.org/10.1063/1.1866635 (3 pages) | Cited 45 times

Online Publication Date: 10 February 2005

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The lifetime of photogenerated carriers in silicon-on-insulator rib waveguides is studied in connection with the optical loss they produce via nonlinear absorption. We present an analytical model as well as two-dimensional numerical simulation of carrier transport to elucidate the dependence of the carrier density on the geometrical features of the waveguide. The results suggest that effective carrier lifetimes of ⩽ 1 ns can be obtained in submicron waveguides resulting in negligible nonlinear absorption. It is also shown that the lifetime and, hence, carrier density can be further reduced by application of a reverse bias pn junction.
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42.82.Et Waveguides, couplers, and arrays
85.30.De Semiconductor-device characterization, design, and modeling
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Comparison of the optical gain of InGaAsN quantum-well lasers with GaAs or GaAsP barriers

H. Carrère, X. Marie, J. Barrau, and T. Amand

Appl. Phys. Lett. 86, 071116 (2005); http://dx.doi.org/10.1063/1.1864253 (3 pages) | Cited 11 times

Online Publication Date: 10 February 2005

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We have compared the calculated band structure and optical gain of compressively strained InGaAsN quantum-well lasers emitting at 1.3 μm with GaAs or GaAsP barriers. The GaAsP barriers yield a better hole confinement in the quantum well due to GaAsP larger band gap. We show that this can result in an increase of the material gain of more than 40% at device operating temperature, which can be explained by the reduction of the hole leakage out of the quantum well.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells
73.20.At Surface states, band structure, electron density of states
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Design and holographic fabrication of tetragonal and cubic photonic crystals with phase mask: toward the mass-production of three-dimensional photonic crystals

Y. Lin, P. R. Herman, and K. Darmawikarta

Appl. Phys. Lett. 86, 071117 (2005); http://dx.doi.org/10.1063/1.1865329 (3 pages) | Cited 25 times

Online Publication Date: 10 February 2005

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We present design and holographic fabrication of the woodpile-type photonic crystals through phase mask techniques. Three-dimensional photonic crystal structures with tetragonal or cubic symmetries are fabricable by exposing the photoresist to the interference patterns generated by the phase masks. These photonic crystals have full photonic band gaps as large as 27% of the gap center frequency if made from silicon. The realized photonic crystal in SU-8 photoresist shows overlapped thus more stable woodpile-type structures. The phase-mask based lithography for the fabrication of the photonic crystals, together with the computer-controlled fabrication process, could take advantage of the standard tools of the electronics industry, leading toward the mass-production of the three-dimensional photonic crystals.
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42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.40.My Applications

Photocurrent spectroscopy analysis of widely tunable negative-chirp quantum-well intermixed laser-modulator transmitters

G. B. Morrison, J. W. Raring, E. J. Skogen, C. S. Wang, and L. A. Coldren

Appl. Phys. Lett. 86, 071118 (2005); http://dx.doi.org/10.1063/1.1865330 (3 pages) | Cited 1 time

Online Publication Date: 10 February 2005

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High-speed laser-modulator transmitters fabricated using InGaAsP quantum-well intermixing exhibit negative chirp over a wavelength range of more than 30 nm. Photocurrent spectroscopy is used to examine the multiple band edges in these devices. An exciton peak is found in the photocurrent data, and the evolution of the band edge as a function of quantum-well intermixing and applied bias voltage is revealed. The photocurrent data are then exploited to verify and explain the negative chirp characteristics of the wavelength-agile transmitters.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Hp Optical processors, correlators, and modulators
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
78.20.Jq Electro-optical effects
72.40.+w Photoconduction and photovoltaic effects
42.60.Fc Modulation, tuning, and mode locking
73.21.Fg Quantum wells
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Submillisecond switching of nematic liquid crystal in cells fabricated by anisotropic phase-separation of liquid crystal and polymer mixture

Qingbing Wang and Satyendra Kumar

Appl. Phys. Lett. 86, 071119 (2005); http://dx.doi.org/10.1063/1.1861120 (3 pages) | Cited 11 times

Online Publication Date: 11 February 2005

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Liquid crystal (LC) cells consisting of a very thin (submicrometer) nematic LC layer switch with time response smaller than 1 ms. The total response time, i.e., sum of the turn-on and turn-off times, can be made as small as 1.3 ms. Such devices were prepared by a photoinduced anisotropic phase separation of mixtures of the LC and prepolymer. The formation of the LC–polymer bilayer in these devices was confirmed by polarized light microscopy and scanning electron microscopy. The phase separation method permits one to fine-tune the LC film thickness by varying the LC concentration in the mixture. This technique can be used to fabricate fast LC devices for TV and video applications.
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42.79.Kr Display devices, liquid-crystal devices
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
64.75.-g Phase equilibria
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Efficient polarized injection luminescence in forward-biased ferromagnetic-semiconductor junctions at low spin polarization of current

A. M. Bratkovsky and V. V. Osipov

Appl. Phys. Lett. 86, 071120 (2005); http://dx.doi.org/10.1063/1.1867558 (3 pages) | Cited 3 times

Online Publication Date: 11 February 2005

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We consider electron tunneling from a nonmagnetic n-type semiconductor (n‐S) into a ferromagnet (FM) through a very thin forward-biased Schottky barrier resulting in efficient extraction of electron spin from a thin n‐S layer near FM‐S interface at low spin polarization of the current. We show that this effect can be used for an efficient polarization radiation source in a heterostructure where the accumulated spin-polarized electrons are injected from n‐S and recombine with holes in a quantum well. The radiation polarization depends on a bias voltage applied to the FM‐S junction.
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73.30.+y Surface double layers, Schottky barriers, and work functions
72.25.Mk Spin transport through interfaces
72.25.Hg Electrical injection of spin polarized carriers
73.63.Hs Quantum wells
73.40.Gk Tunneling
73.40.Ns Metal-nonmetal contacts

Effect of nitrogen on gain and efficiency in InGaAsN quantum-well lasers

D. J. Palmer, P. M. Smowton, P. Blood, Jeng-Ya Yeh, L. J. Mawst, and Nelson Tansu

Appl. Phys. Lett. 86, 071121 (2005); http://dx.doi.org/10.1063/1.1868070 (3 pages) | Cited 8 times

Online Publication Date: 11 February 2005

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We compare the gain and radiative efficiency characteristics of an InGaAsN and an InGaAs laser structure where the devices are identical except for the nitrogen content and emission wavelength. We find that the inclusion of nitrogen has little impact on the gain spectra except for the required shift to longer wavelength and that the intrinsic gain-radiative current characteristics may be slightly better for the nitrogen-containing materials. The radiative efficency is reduced by a factor of 4 in the samples containing nitrogen due to increased nonradiative recombination.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Improved spatial resolution and surface roughness in photopolymerization-based laser nanowriting

Kenji Takada, Hong-Bo Sun, and Satoshi Kawata

Appl. Phys. Lett. 86, 071122 (2005); http://dx.doi.org/10.1063/1.1864249 (3 pages) | Cited 66 times

Online Publication Date: 11 February 2005

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The fundamental issues on the smallest possible processing accuracy and the best feasible surface smoothness in pinpoint polymerization-based laser fabrication were experimentally investigated. The lateral spatial resolution is improved from the previously reported value, 120 nm, to around 100 nm by intentionally introducing radical quenchers in the resin. The roughness measured from 10 μm×10 μm surface areas were averaged to 4–11 nm, which is found slightly affected by the laser pulse energy but independent on the scanning pitch when it is smaller than a critical value. The surface quality of this level could fully satisfy the requirement of various photonic elements and devices.
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68.55.-a Thin film structure and morphology
81.16.Mk Laser-assisted deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.50.-m Photochemistry
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Predicted properties of microhollow cathode discharges in xenon

J. P. Boeuf, L. C. Pitchford, and K. H. Schoenbach

Appl. Phys. Lett. 86, 071501 (2005); http://dx.doi.org/10.1063/1.1862781 (3 pages) | Cited 57 times

Online Publication Date: 7 February 2005

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A fluid model has been developed and used to help clarify the physical mechanisms occurring in microhollow cathode discharges (MHCD). Calculated current-voltage (I-V) characteristics and gas temperatures in xenon at 100 Torr are presented. Consistent with previous experimental results in similar conditions, we find a voltage maximum in the I-V characteristic. We show that this structure reflects a transition between a low-current, abnormal discharge localized inside the cylindrical hollow cathode to a higher-current, normal glow discharge sustained by electron emission from the outer surface of the cathode. This transition, due to the geometry of the device, is a factor contributing to the well-known stability of MHCDs.
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52.80.Hc Glow; corona
52.25.Fi Transport properties
52.25.Tx Emission, absorption, and scattering of particles
52.25.Jm Ionization of plasmas
52.65.-y Plasma simulation

Interaction of a laser-produced plume with a second time delayed femtosecond pulse

D. Scuderi, O. Albert, D. Moreau, P. P. Pronko, and J. Etchepare

Appl. Phys. Lett. 86, 071502 (2005); http://dx.doi.org/10.1063/1.1864242 (3 pages) | Cited 32 times

Online Publication Date: 11 February 2005

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Time resolved emission spectroscopy coupled with a secondary time-delayed femtosecond pulse technique has been used to study laser–matter interaction that occurs within ablation processes from a solid target, in the 1012–1014 W/cm2 energy range. It allows an examination of the emitted optical signals that characterize the species escaping from the target, namely ions, neutrals, and nanoparticles. Size distributions of nanoparticles are deduced from an analysis of the deposition substrate. The newest result concerns the huge drop of emission signal from the nanoparticles, which occurs at a delay (0.8<Δt<1 ns) and has been attributed to a fragmentation process.
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78.47.-p Spectroscopy of solid state dynamics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.62.-b Laser applications
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Shallow electronic states induced by prismatic stacking faults in AlN and GaN

J. E. Northrup

Appl. Phys. Lett. 86, 071901 (2005); http://dx.doi.org/10.1063/1.1866510 (3 pages) | Cited 3 times

Online Publication Date: 7 February 2005

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Wurtzite materials such as AlN and GaN can exhibit prismatic stacking faults on the (1-210) plane with a stacking fault displacement vector RD = 1/2[10-11]. These faults thread in the [0001] direction and may arise in growth on the (0001) plane from the merging of independently nucleated islands. Merging islands that have different stacking sequences in the [0001] direction, for example ABAB… vs ACAC…, give rise to the faults. The formation energy of such a stacking fault in AlN is determined using first-principles total energy calculations to be 79 meV/Å2. The perturbation caused by the highly strained four-membered rings of bonds along the boundary gives rise to shallow stacking fault states 0.1 eV above the valence band maximum and 0.1 eV below the conduction band minimum. These results are compared to those obtained for GaN.
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71.15.Nc Total energy and cohesive energy calculations
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
61.72.Nn Stacking faults and other planar or extended defects
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
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